Studies in our laboratories have indicated that Resonance Raman (R.R.) spectroscopy of chromophores bound to biomacromolecules is useful for determination of binding interactions. Using this technique we have determined the ionization state, conformation, metal-ligand interaction and other structural details of the chromophore bound to a biomacromolecule. We have obtained R.R. spectra of flavins and flavoproteins at concentration of 1 times 10 to the minus 4th power minus 1 times 10 to the minus 3rd power M. The fluorescence interference of flavins in solution is overcome by the use of KI as a collisional quenching agent, and the fluorescence in many flavoproteins is low due to quenching by the protein. We are studying the R.R. spectra of a variety of flavoproteins involved in beta-oxidation of fatty acyl CoA esters. Raman spectroscopy on fatty acyl CoA dehydrogenase has proven important in investigation of hydrogen bonding between the N-3 hydrogen on the FAD and the protein. R.R. spectral data suggest that FAD bound to enzyme is in a poorer hydrogen bonding environment than aqueous FAD. We have studied the acetoacetyl CoA charge transfer complex of fatty acyl CoA dehydrogenase and have observed R.R. spectral intensity changes in the 1630 cm to the minus 1st power and 1580 cm to the minus 1st power regions of the spectrum. These changes have led to important conclusions concerning that portion of the FAD molecule which interacts with ligand in these charge transfer complexes. Finally, we have investigated the R.R. spectrum of metal flavin complexes, and we have shown that R.R. spectra are excellent probes of metal flavin interaction. We are pursuing these studies in order to understand protein-flavin interactions in flavoenzymes.